1. Field of The Invention
The invention relates to indicating instruments, and more particularly to a primary flight director instrument having a pitch cue responsive to resolution advisory guidance commands for collision avoidance.
2. Description of The Prior Art
The Traffic Advisory and Collision Avoidance System (TCAS) uses a Mode S Transponder with which civilian and military aircraft are equipped to communicate collision avoidance decisions between aircraft. One form of TCAS, known as TCAS II, is intended for large commercial and general aviation aircraft. Aircraft in proximity are tracked in both the horizontal and vertical planes, from which the time of closest approach may be predicted. However, the lack of adequate bearing measurement accuracy precludes support of horizontal maneuvers. The pilot of the own aircraft is advised on how to avoid a collision with respect to advisories to climb, descend, do not climb, or do not descend, and may also be advised as to a required vertical speed rate to avoid a collision. If the threat aircraft is also equipped with a TCAS system, the avoidance maneuver will be communicated and coordinated with the threat aircraft accordingly, so that both aircraft do not select the same avoidance maneuver.
Threat detection is performed at two levels. When air traffic approaches within a predetermined protective volume a traffic advisory is provided to alert the pilot to attempt a visual sighting and take whatever corrective action he deems appropriate to increase separation between the aircraft. If the two aircraft continue to approach, typically such that within a minimum time of 20 seconds they will be within 0.1 nautical mile (n) of each other and with an altitude difference not greater than 750 ft, a resolution advisory will be issued, displaying a maneuver to the pilot to increase separation of the aircraft. The advisories may be accompanied by limits to the rate of climb or descent.
Prior art resolution advisory displays have been in the form of a mechanical instrument or electronic display providing a pointer on an altitude rate scale and an arrow or colored scale for displaying change in altitude advisories. See, for example, U.S. Pat. No. 4,914,733 and U.S. Pat. No. 3,621,210. However, such displays have heretofor not provided command information for changes in pitch attitude necessary to satisfy the resolution advisory.
Aircraft primary flight director instruments are well known for use in providing visual commands to the pilot. Thrust, pitch attitude, and bank attitude controls are exercised by the human pilot while observing the flight director display. When the pilot manipulates the aircraft controls in a manner to keep the steering cues aligned with corresponding fixed reference symbols, he will satisfy the pitch and roll attitude control law so that the aircraft is maintained on a predetermined flight path.
Such flight director steering cues have in general been provided in two forms--steering bars, adapted for movement up or down to command corresponding changes in pitch and for movement left or right to command bank angle changes, and aircraft symbols, representative of the attitude of the aircraft, which move up and down to command pitch changes and roll left or right to command bank angle changes.
The present invention provides an indicator for a primary flight director instrument display which is provided with a single cue provided in pitch to provide visual commands for bringing the craft to a pitch attitude commensurate with the resolution advisory vertical velocity signal. It overcomes the disadvantage of purely performance cues such as vertical velocity, in which the performance cue display may lag the current vertical speed.
A single cue provides both a pitch change command and indicates a guarded region to be avoided. A further cue provides the current vertical speed in a numerical display as well as bands indicating a target vertical velocity and a proscribed vertical velocity range. The instrument further provides the capability of indicating pitch commands in the presence of two threat aircraft.